Lapping and grinding machines have been utilized to manipulate the flatness of surfaces for subsequent use in mechanical and hydraulic mechanisms. The purpose of this manipulation operation is to make a surface of a part, typically metal, as smooth as possible. An example would be the opposing surfaces of the rotor utilized in the White Hydraulics, Inc. Motor as represented in White U.S. Pat. No. 5,135,369. In this example application, by flattening the opposing surfaces of the rotor, the volumetric and mechanical efficiency of the device can be increased by maintaining tighter spacing and tolerances between the flat surfaces of the rotor and adjoining surfaces of the motor housing.
In prior art two wheel grinding devices, a parts carrier assembly is located between two iron lapping wheels (it is called ‘lapping’ because the fine grinding particles are located in a surry and not the actual movable wheels). An example is the Hahn and Kolb Model ZL801 lapping machine. In this machine a carrier assembly consisting of a fixed outer stator, a driven inner pinion and toothed planet wheels are located between two iron lapping wheels. The parts to be lapped are located in sockets in the toothed planet wheels.
The iron lapping wheels themselves are initially dressed by a separate wheel dressing unit. The machine itself includes a source of the main cutting material, for example a silicon carbide surry, that accomplishes the actual lapping function. In the lapping operation, the devices typically operate under Rule 141 (New), double lap flatness of wheels. According to Rule 141, the flatness of the iron lapping wheels are periodically tested by the operator with a straight edge across the surface of each wheel. If one wheel in concave or low in the center, and the other wheel is convex or high in the center, then the wheels are run opposed to each other with the carrier run with the wheel which is low in the center. If both wheels are low in the center, both wheels and the center carrier are run in the same direction. If both wheels are high in the center, the wheels are run in the same direction with the carrier run in a direction opposed to the wheels. The actual rotational speed of the wheels is selected in consideration with the sizing of the work together with the amount of material to be removed.
Operations under Rule 141 require significant operator involvement in the operation of the machine and, in addition, typically an assistant to aid in the testing of the wheels to determine whether the wheels are low in the center or high in the center. In addition, the surry takes the same amount of material off of the iron lapping wheels as the parts being operated on by the machine.
The relative flatness of the lapping operation is thus normally interconnected with the tolerances of the machine together with the skill of the setup operator.
In respect to fine grinding wheels, it is necessary to periodically remove such wheels to flatten their grinding surfaces. This interrupts production while subjecting the grinding wheels to the risk of damage.